In 1895 he opened an office in Bedford with George Grocock and worked in the Arts and Crafts tradition designing cottages, schools, shops and restoring churches including the Trinity chapel of St Paul's Church, Bedford.
He was made a fellow of the Royal Institute of British Architects in 1900 and by the following year was the diocesan surveyor for Ely.
Mallows rented rooms adjoining those of the landscape architect Thomas Hayton Mawson, and occasionally worked with him.
He died on 2 June 1915 at his home in Biddenham, Bedfordshire[1] leaving an estate of nearly £3,000.
From 1914 until his death, Mallows designed the house and gardens at Craig-y-parc, Pentyrch, Glamorgan, for the colliery owner Thomas Evans.